JAKs are kinases which phosphorylate a group of proteins called Signal Transduction and Activators of Transcription or STATs. When phosphorylated, STATs dimerize, translocate to the nucleus and activate expression of genes which lead to, amongst other things, cellular proliferation such as proliferation of endothelial cells and smooth muscle cells, and cause hypertrophy of cardiac myocytes.
A review of the JAK/STAT literature offers strong support to the hypothesis that this pathway is important for the recruitment and marshalling of the host immune response to environmental insults, such as viral and bacterial infection. Information accumulated from gene knock-out experiments have underlined the importance of members of the JAK family to the intracellular signalling triggered by a number of important immune regulatory cytokines. The therapeutic possibilities stemming from inhibition (or enhancement) of the JAK/STAT pathway are thus in the sphere of immune modulation, and as such are likely to be promising drugs for the treatment of a range of pathologies in this area. In addition inhibitors of JAKs could be used for immunological and inflammatory diseases including organ transplants, asthma and chronic obstructive pulmonary disease (COPD) as well as autoimmune diseases such as systemic lupus erythematosus, mixed connective tissue disease, scleroderma, autoimmune vasculitides, multiple sclerosis, rheumatoid arthritis, Crohns disease, Type I diabetes and autoimmune thyroid disorders.
The central role played by the JAK family of protein tyrosine kinases in the cytokine dependent regulation of both proliferation and end function of several important cell types indicates that agents capable of inhibiting the JAK kinases are useful in the prevention and chemotherapeutic treatment of disease states dependent on these enzymes. Potent and specific inhibitors of each of the currently known four JAK family members will provide a means of inhibiting the action of the cytokines that drive immunological and inflammatory diseases, such as those discussed above. Additionally, treatment of hyperproliferative disorders such as cancers including multiple myeloma; prostate, breast and lung cancer; Hodgkin's Lymphoma; B-cell Chronic Lymphocytic Leukemia; metastatic melanoma; glioma; and hepatoma, by JAK inhibitors is indicated. Additionally the use of JAK kinase inhibitors for the treatment of viral diseases and metabolic diseases is indicated.
Potent inhibitors of JAK2, in addition to the above, will also be useful in vascular disease such as hypertension, hypertrophy, cardiac ischemia, heart failure (including systolic heart failure and diastolic heart failure), migraine and related cerebrovascular disorders, stroke, Raynaud's phenomenon, POEMS syndrome, Prinzmetal's angina, vasculitides, such as Takayasu's arteritis and Wegener's granulomatosis, peripheral arterial disease, heart disease and pulmonary arterial hypertension. JAK2 inhibitors will also be useful in myeloproliferatve disorders (MPD) such as polycythemia rubra vera (PCV).
Potent and specific inhibitors of both JAK1 and JAK2 will be useful in the treatment of cancers including multiple myeloma; prostate, breast and lung cancer; Hodgkin's Lymphoma; B-cell Chronic Lymphocytic Leukemia; metastatic melanoma; glioma; and hepatoma.
Potent and specific inhibitors of JAK3 will be useful as immunosuppressive agents for, amongst others, organ transplants, and immunological and inflammatory diseases such as asthma and chronic obstructive pulmonary disease as well as autoimmune diseases such as systemic lupus erythematosus, mixed connective tissue disease, scleroderma, autoimmune vasculitides, multiple sclerosis, rheumatoid arthritis, Crohn's disease, Type I diabetes and complications from diabetes, metabolic diseases, and other indications where immunosuppression may be desirable. Furthermore specific inhibitors of JAK3 may find application for therapeutic treatments for proliferative diseases such as leukaemia and lymphoma where JAK3 is hyperactivated.
Although the other members of the JAK family are expressed by essentially all tissues, JAK3 expression appears to be limited to hematopoetic cells. This is consistent with its essential role in signalling through the receptors for IL-2, IL4, IL-7, IL-9 and IL-15 by non-covalent association of JAK3 with the gamma chain common to these multichain receptors. Males with X-linked severe combined immunodeficiency (XSCID) have defects in the common cytokine receptor gamma chain (gamma c) gene that encodes a shared, essential component of the receptors of interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15. An XSCID syndrome in which patients with either mutated or severely reduced levels of JAK3 protein has been identified, suggesting that immunosuppression should result from blocking signalling through the JAK3 pathway. Gene Knock out studies in mice have suggested that JAK3 not only plays a critical role in B and T lymphocyte maturation, but that JAK3 is constitutively required to maintain T cell function. Taken together with the biochemical evidence for the involvement of JAK3 in signalling events downstream of the IL-2 and IL-4 receptor, these human and mouse mutation studies suggest that modulation of immune activity through the inhibition of JAK3 could prove useful in the treatment of T-cell and B-cell proliferative disorders such as transplant rejection and autoimmune diseases.
Prolonged immunomodulation through inhibition of JAK3 signalling should have great therapeutic potential for chronic diseases as long as JAK3 inhibition was achieved selectively and not accompanied by inhibition of other kinase-dependent signalling processes. In particular, the high degree of sequence identity held in common by members of the JAK family of kinases raises the possibility that a compound which inhibits JAK3 would also inhibit other members of the family with detrimental long term consequences. For example, prolonged inhibition of JAK2 is likely to lead to erythropenia and thrombocytopenia, since the receptors for both erythropoietin and thrombopoietin use only JAK2 for intracellular transmission of signals.
Compounds of the present invention may also be useful in targeting other kinases of therapeutic relevance, such as the Aurora kinases. The Aurora family of serine/threonine protein kinases are critical for the proper regulation of mitosis. Mammals express three Aurora kinase paralogs, and at least two Aurora kinases (Aurora A and B) are commonly overexpressed in human tumours including breast, lung, colon, ovarian, and pancreatic cancers. The Aurora A gene is amplified in many tumours, indicating that overexpression of Aurora A may confer a selective advantage for the growth of these tumours. Overexpression of Aurora B has also been reported to produce multi-nuclearity and induce aggressive metastasis, suggestion that the overexpression of Aurora kinase B has multiple functions in cancer development. Recent clinical experience and subsequent approvals of kinase inhibitors such as Imatinib, Gefitinib and Erlotinib illustrate that this class of enzymes will be useful for anticancer drug development. Aurora A itself has been identified as a particularly attractive drug target through observations that it can act as an oncogene and transform cells when ectopically expressed. VX-680, a potent inhibitor of Aurora A and B kinases, has been shown to suppress tumour growth in vivo. These findings highlight the desirability of identifying Aurora kinase inhibitors for use in cancer treatment.
Other kinases which may be useful therapeutic targets include CK2, TBK1, NEK9, LCK, ACK1, p38 kinase, FAK, CAK, CDK4, GSK-3, Abl, PDGF-R, PLK1, PLK2, PLK3, PYK2, c-Kit, NPM-ALK, Flt-3, c-Met, KDR, EGFR, TIE-2, VEGFR-2, VEGFR-3, FMS, HCK, Blk, Bmx, BTK, Flt-1 and Flt-4.
Although the inhibition of various types of protein kinases, targeting a range of disease states, is clearly beneficial, it has been to date demonstrated that the identification of a compound which is selective for a protein kinase of interest, and has good “drug like” properties such as high oral bioavailability, is a challenging goal. In addition, it is well established that the predictability of inhibition, or selectivity, in the development of kinase inhibitors is quite low, regardless of the level sequence similarity between the enzymes being targeted.
The challenges in developing a therapeutically appropriate JAK1, JAK2 or JAK3 inhibitors or combinations thereof for use in treatment of kinase associated diseases such as immunological and inflammatory diseases including organ transplants; hyperproliferative diseases including cancer and myeloproliferative diseases; viral diseases; metabolic diseases; and vascular diseases, include designing a compound with appropriate specificity which also has good drug likeness.
There is therefore a continuing need to design and/or identify compounds which specifically inhibit the JAK family of kinases, and particularly compounds which may preferentially inhibit one or more of the JAK kinases relative to the other JAK kinases. There is a need for such compounds for the treatment of a range of disease states.